The invention, in some embodiments, relates to the field of detection devices and more particularly, in some embodiments, to passive detection devices and methods using electromagnetic radiation having millimeter wavelengths.
Detection of objects obscured from view is a long standing need in various fields such as in defense and security, medicine, industry and transportation. An object may be obscured from view if it is prevented from reflecting or emitting light, such as when located in a dark room, or if located behind an opaque or light-scattering medium, such as when located in fog or smoke, or when located on the body of a person and obscured behind clothing.
As is well known in the art of detection devices, an object emits electromagnetic radiation with an intensity that is dependent on the temperature and the emissivity of the object. An object at a lower temperature emits less radiation than the same object at a higher temperature and, at equal temperatures, an object having a higher emissivity emits more radiation than an object having a lower emissivity.
This characteristic of electromagnetic radiation has been used to create imaging devices configured to provide images of objects using non-visible electromagnetic radiation (e.g., IR, X-ray), which devices are often used for detecting concealed objects. However, the use of such devices, particularly in contexts such as homeland security, is limited or prohibited due to physical constraints, safety regulations, privacy violation limitations, physical size and high cost.
Detection devices operating in the millimeter-wave range of electromagnetic radiation, that is radiation having wavelengths in the range of 1 to 10 millimeter which corresponds to frequencies of 30 to 300 GHz, overcome some of the problems presented by detection devices using electromagnetic radiation having wavelengths in other ranges.
Specifically, millimeter-wave electromagnetic radiation can penetrate many screening materials, such as fog, smoke, carton, sheets of plastic, and clothing. Additionally, millimeter-wave detection allows for millimeter-scale detection resolution. Furthermore, with respect to millimeter-wave radiation, the attenuation and reflection characteristics of ceramic, metallic, and plastic weapons, as well as contrabands such as narcotics, are different from the characteristics of human skin, thereby enabling detection of such objects concealed on a person's body.
Publications related to the use of millimeter-wave radiation in the field of detection devices include: U.S. Pat. No. 5,073,782; U.S. Pat. No. 5,760,397; U.S. Pat. No. 6,777,684; U.S. Pat. No. 6,950,054; U.S. Pat. No. 6,967,612; US 2005/0099330; US 2009/0195435 as well as the non-patent publications:    Appleby R in “Passive Millimeter-Wave Imaging and How It Differs From Terahertz Imaging,” Phil Trans R Soc, London, A (2004) 362, 379-394;    Yujiri L, Shoucri M, Moffa P in “Passive Millimeter Wave Imaging,” IEEE Microwave Magazine 2003, September, 39-50;    Manasson V A, Sadovnik L S, Mino R, Rodionov S in “Novel Passive Millimeter Wave Imaging System: Prototype Fabrication and Testing” Passive Millimeter-Wave Imaging Technology, Proc. SPIE Optical Engineering 2000, v. 5070, 21 April, 2-13;    Kapilevich B, Litvak B, Einat M, Shotman O in “Passive mm-Wave Sensor for Indoor and Outdoor Homeland Security Applications” Proc. 2007 International Conference on Technologies and Applications, Spain, 20-23;    Sheen D M, McMakin D L, Hall T E in “Three-Dimensional Millimeter-Wave Imaging for Concealed Weapon Detection,” IEEE Transactions On Microwave Theory and Techniques 2001, v. 49, n. 9, 1581-1592;    Sheen D M, McMakin D L, Lechelt W M, Griffin J W in “Circularly Polarized Millimeter-Wave Imaging For Personnel Screening” Proc. SPIE Optical Engineering 2005, v. 5789, 21, April, 117-126;    Kapilevich B, Einat M, Litvak B, Shulsinger A, Nehemia E in “Experimental Study of Indoor mm-Wave Imaging Resolution Limits” Workshop Nefertiti-2005, Brussels, paper #111;    Boykin R D in “A Brief Overview of T-ray (THz) Imaging”, DX2 Report, May 12, 2005, http://ric.uthscsa.edu/personalpages/lancaste/DI2_Projects—2005/T-Ray.pdf;    Cooper K B, Dengler R J, Chattopadhyay G, Schlecht E, Gill J, Skalare A, Mehdi I, Siegel P H in “A High-Resolution Imaging Radar at 580 GHz”, IEEE microwave and wireless components letters 2008, v. 18, n. 1, January, 64-66;    Dickinson J C, Goyette T M, Gatesman A J, Joseph C S, Root Z G, Giles R H, Waldman J, Nixon W E, “Terahertz imaging of subjects with concealed weapons” Proc. SPIE 2006, vol. 6212, 62120Q01-62120Q12;    Kemp M C, Taday P F, Cole B E, Cluff J A, Fitzgerald A J, Tribe W R, “Security Applications of Terahertz Technology,” Proc. SPIE 2003, v. 5070, 44-52;    Petkie D T, DeLucia F C, Casto C, Helminger P, Jacobs E L, Moyer S K, Murrill S, Halford C, Griffin S, Franck C in “Active and Passive Millimeter and Sub-Millimeter-Wave Imaging,” Proc. SPIE 2005, v. 5989, 598918-1-598918-8;    Tryon G, “Passive Millimeter-Wave Object Detection and People Screening”, presentation at 2007 SURA Terahertz Applications Symposium June 6-8, Washington, D.C.; and    McMillan R W, Currie N C, Ferris D D, Wicks M C Jr. in “Concealed Weapon Detection Using Microwave and Millimeter Wave Sensors” Microwave and Millimeter Wave Technology Proc 1998 ICMMT'98, 1-4.
A challenge is how to practically make use of the advantages of millimeter-wave radiation in the field of detection devices.